1. Field of the Invention
The invention pertains to a method for determining the absolute angular position of the steering wheel of a motor vehicle. The invention specifically pertains to a method in which a control unit continually reads in first angle measurement values that are physically acquired by a sensor unit associated with the control unit at a constant first interval, wherein the control unit additionally processes and outputs the angle measurement values in the form of coded output values via an output interface.
2. Background Art
The absolute angular position of the steering wheel of a motor vehicle, which is also referred to as the steering angle, is, for example, required for influencing a dynamic control system. In addition to the above-mentioned steering angle, such a dynamic control system receives other measurement data, e.g., the rotational speed of the wheels or the rotation of the motor vehicle about its vertical axis. The absolute steering deflection angle, as well as the steering speed, are evaluated by the dynamic control system together with other acquired data and used for controlling actuators, for example, of the brakes and/or the engine management.
An optoelectronic steering angle sensor for realizing such a method is known from DE 40 22 837 A1. The steering angle sensor described in this document consists of an electronic control unit and a sensor unit with two elements that are arranged parallel to and spaced apart from one anotherxe2x80x94namely a light source and a line sensor. This steering angle sensor also contains a code disk that is arranged between the light source and the line sensor and connected to the steering spindle without rotational play. In this case, a CCD sensor line is used as the line sensor. The coding of this code disk consists of a light slot that is realized in the form of an Archimedean spiral and extends over 360xc2x0. Information on the actual steering angle can be obtained based on the illumination of the corresponding transducer elements of the line sensor at a certain steering deflection. The Archimedean spiral used as the coding extends continuously, i.e., this coding consists of an analog coding. However, this arrangement would also be suitable for reading a digital coding on the code disk, for example, in the form of a Gray code.
The output rate of the measurement values in such a steering angle sensor is generally defined by the dynamic control system of higher order. This means that an angle measurement value is physically acquired by the sensor unit at usually constant intervals (e.g., every 10 msec), additionally processed, and output to the dynamic control system in the form of a coded output value via an output interface.
Due to this fixed output rate, the angle traveled between two measurements increases proportionally with the angular velocity of the steering wheel. However, this significantly limits the reliability of control methods that usually serve for controlling the proper function of such systems and are based on plausibility criteria, specifically because a continuously increasing difference between two successively measured angles must be accepted to be correct as the angular velocity increases.
Based on the previously discussed state of the art, the invention aims additionally to develop a method of the initially described type in such a way that reliable angle measurement that can be verified by means of plausibility criteria is also possible at high angular velocities of the steering wheel.
According to the invention, this objective is attained due to the fact that at least a second angle measurement value is read in by the control unit for each output value, wherein a second interval that is shorter than the first interval lies between the procedure of reading in the first angle measurement value and the procedure of reading in the second angle measurement value associated with the first angle measurement value.